Stabilization of mercaptans



Patented June 22, 1948 STABILIZATION OF MEBCAPTANS comes J. Peder-sen,

to E. I. du Pont de Penna Grove, N. 1., assignor Nemours & Company,Wilmington, Del., a corporation of Delaware No Drawing.

14 Claims.

This invention relates to the stabilization of mercaptans andparticularly to inhibiting the oxidation of mercaptans in the presenceof iron and its catalytically active compounds.

In general, mercaptans are susceptible to oxidation by the oxygen of theair during manufacture and storage, whereby they are oxidized to thecorresponding disulfldes. This oxidation is catalyzed by iron, manganeseand copper and many of their compounds. The catalysis of such oxidationby iron is particularly unfortunate since most production equipment andstorage vessels are made of ferrous metals, whereby the mercaptans arefrequently exposed to contamination by iron.

It is an object of my invention to stabilize mercaptans againstoxidation during manui'acture and storage. Another object is tostabilize mercaptans against oxidation, particularly when suchmercaptans contain or are in contact with iron or its catalyticallyactive compounds. A further object is to provide novel stabilizers formercaptans. Other objects are to provide new compositions of matter.Still other objects will appear hereinafter.

The above and other objects may be accomplished in accordance with myinvention which comprises incorporating in a mercaptan, normally subjectto oxidation by the oxygen of the air, a small proportion, sufficient toinhibit such oxidation, of an organic compoimd containing a radical ofan oxygen acid of phosphorus having at least one unreplaced acidhydrogen atom. I have found that such phosphorus compounds are veryeffective to stabilize the mercaptans against oxidation, particularlywhen the mercaptan contains or is in contact with iron or acatalytically active compound of iron. These phosphorus compounds alsovery substantially reduce the corrosive action of the mercaptans onferrous metals.

A mercaptan, as employed herein, will be understood to mean an organiccompound containing an SH group with the sulfur directly bonded tocarbon. The mercaptan may be an open chain aliphatic mercaptan, acycle-aliphatic mercaptan, an aromatic mercaptan (a thiophenol) or aheterocyclic mercaptan. The mercaptan may contain non-hydrocarbongroups, such as hydroxyl, ether, thioether, carboxylic ester, carboxylicamide, thiazyl, thiazolinyl and like groups. However, my invention isparticularly applicable to mercaptans which, except for the SH group,consist oi. carbon and hydrogen and especially to the aliphaticmercaptans which may be acyclic or alicyclic.

I have iound that organic compounds containing a radical of an oxygenacid 01 phosphorus,

Application December 14, 1944, Serial No. 568,214

having at least one um'eplaced acid hydrogen atom, are, as a class,efiective to materially inhibit oxidation of such mercaptans. Suchphosphorus compounds may be represented by the formula.

wherein It represents an aliphatic, aromatic, aliphatic oxy or aromaticoxy radical; R represents hydrogen or an aliphatic or aromatic radical;M represents P or P=0. Representative types of compounds within thisclass are:

Organic phosphonic acids Organic phosphinic acids Organic acid-esters ofphosphoric acids Organic acid-esters oi phosphorous acid Organicacid-esters of phosphonic acids I particularly prefer the organicacid-esters of the oxygen acids of phosphorus and especially ofphosphoric acid. Also, I generally prefer that the organic group,attached to the radical of the acid of phosphorus, be an aliphaticradical and especially a long chain aikyl radical. By long chain, 1 meana chain of at least 8 carbon atoms. The most desirable and effective ofthe phosphorus compounds is the mixture designated as "Lorol phosphate.This is a mixture of monoand di-esters derived from Lorol" alcohol.Lorol alcohol is a commercial mixture of normal straight-chain alcohols,consisting primarily of n-octyl and n-decyl alcohols, and is obtained bythe fractionation of the mixtures of alcohols resulting from thereduction of cocoanut or palm kernel oils.

The phosphorus compounds or stabilizers may be employed within a widerange of concentrations generally of from about 0.001% to about 1%, butpreferably will be employed in the proportion of from about 0.005% toabout 0.1% based on the mercaptan. The stabilizers may be added directlyto the mercaptan or dissolved in a suitable solvent. They may be addedto the mercaptan at any suitable step in its process of manufacture.

The relative oxidation stability of the thiol compounds, or mercaptans,was determined by two difierent experimental methods: (1) oxygenabsorption at room temperature, and (2) accelerated aging at 66:1" C.

The equipment for the first method consisted of an upright stoppereddistilling flask (340 cc. capacity) connected to a 780 mm. verticalglass tube which dipped into a reservoir of mercury. The flask wasflushed with commercial oxygen for 5 minutes, charged with the sample(50 cc.)

Tana: I

Oxygen absorption by "L01'Ol mercaptan Cone. Relative No. Additive Wt.Per- Rate 010; cent Absorption i. None lank) ion 2 Hteai'amdd idomethanephosphonio 0. 01 as B 3- Ironasferriooleate 0.004 1,240

It will be observed that the rate oi oxidation of "Lorel" mercaptan isgreatly increased by soluble iron and retarded by the phosphonlc acid.

The results obtained with pinene mercaptan are given in Table II.

Tm: II

Oxygen absorption by Mnene mercaptan w. sets A t er- N0 v9 centAbsorption oxidation or pinene It will be noted that the mercaptan isaccelerated by iron and retarded by Lorol" phosphate. which is a mixturecomprising monoand di-(n-octyl) phosphates and monoand d-(n-decyl)phosphates. Lei-oi" phosphate is capable of suppressing the catalyticactivity oi iron.

The results obtained with alphaand betathlonaphthols. which aresubstantially in agreement with the results already presented, are

shown in Tables III and IV.

Tasu: In Oxygen absorption by alpha-thionaphthol Cone. Relative No.Additive Wt. Per- Rate 0! 0:

cent Absorption 1. None (blank) 100 2- "Loni" phosphate. 0. l 83 3-.."Ironasiarric oleate. 0.004 3,320 4 mo as ionic else 0. 004 108 Lorol"phosphate 0. 1

Teen: IV Oxygen absorption by beta-thionaphthol Geno. Relative No.Additive Wt. Per- Rate 01 0| cent Absorption 1 Non iank 100 2"-.."Loroi" phosphate- 0. i so 3 Iron as ierrio oieete. 0. 00 1, 240 4 {Ironas i'erric oleate 0. 004 122 "Loroi" phosphate. 0.1

The oxidation stability and the stabilization of "Iorol" mercaptan weretested more extensively by an accelerated test. This method consisted inexposing 50 cc. of mercaptan in a cc. unstoppered glass bottle to theair in a constant temperature oven maintained at 66: 1 0. Small sampleswere taken out periodically and their purity determined iodometrically.The results obtained by this method are given in the following tables.

Tun V Air oxidation of Lorol mercapton at 66: 1 C.

0 Pelrlcent LouDin Pu- 0n0. Altar No. Additive we. Perw m o r is u1.-... None (blank) 0.0 0.0 7.1 0.0 a-.." Dlbntyiphosphits 0.01 0.0 as1.0 2.1 3"..- Benunsphosphonioacid. 0.01 0.0 0.0 0.9 1.9

It will be noted that dibutyi phosphite and benzene phosphonic acidretard the oxidation or Lorol mercaptan. The inhibition due to thesecompounds during 34 days 0! exposure was 74.1 and 77.1%, respectively.

'Taau VI Air oxidation of "Lora!" mercaptan at 6611' c.

Percent Loss in Pur- Oonc. ity Alter Days No. Additive Wt. Percent 1(blank) 0.0 1.0 5.7 0.8 2 Lorci"phosphato 0.01 0.0 0.0 0.4 0.7

Tana: VII

Corrosion of black iron in "Lorol" mercaptan at room temperature 0Corrosion, A

0110. in on N Tmmm Wt. Persig ts. pi 01 55am cent hrs.

1...-.-..- None (blank). 0.42 Clean but not 2... "LoroP'phoa- 0.01 or!Clean and photo. shiny At the end or the corrosion tests the samples oimercaptan were analyzed for purity and exposed to air at 66:1 C. for 6days. After this period they were analyzed again and the percent loss inpurity calculated. The results are shown in the following table.

1 'I'sau: VIII Air oxidation of "Lore!" mcrcapton Percent loss in purityCone cent

Treatment AM roaion test None Wank)..." NM

It will be observed that "Lorol" phosphate not only decreases thecorrosion of iron in "Lorol" mercaptan, but greatly increases theoxidation stability of the mercaptan. As far as the loss of metal isconcerned, the corrosion of iron in Lorol mercaptan at room temperatureis relatively slight. The advantages gained by the use of the phosphateare the better appearance of the metal, and a diminished tendency of themercaptan to oxidize and darken in contact with iron.

The stabilizers belonging to this class can be prepared by the variouswell known methods disclosed in the literature. "Lorol phosphate, forexample is prepared by reacting "Lorol" alcohol with phosphous pentoxideat about fill-60 C.

Besides many others the following compounds are stabilizers ofmercaptans:

Monolauryl phosphite Monobutyl-mono-octyl phosphite Monophenyl phosphateDilauryl phosphate Monobutyl-monodecyl phosphate Lecithin CephalinPhytic acid Benzene phosphinic acid 2-hydroxy-2-propane phosphonic acidl2-hydroxy-12-tricosane phosphonic acid Benzamidomethane phosphonic acidBesides many others, the following mercaptans can be stabilized by meansof the phosphorus compounds of this invention.

Propyl mercaptan Butyl mercaptan Amyl mercaptan Hexyl mercaptan Heptylmercaptan Octyl mercaptan Decyl mercaptan Dodecyl mercaptanMonothiopropylene glycol Propanedithlol-1,2 Z-ethylhexyl thioglycolateDibutylamide of thioglycolic acid Pentadecanedithiol-7,8

Decane dithiol-1,10

Monoethyl ether of ethanedithiol Pinene mercaptan 'I'hioterpineolThioterpinol Thiobomeol Cyclohexyl mercaptan Benzyl mercaptan ThiophenolThiocresol Dithioresorcinol 2-methyl-5-isopropylthiophenolAlpha-thionaphthol Bcta-thionaphthol 2-mercaptobenzothiazole2-mercaptothiazoline and mixtures of these and other mercaptans.

By the practice at the present invention, mercaptans of greatlyincreased oxidation stability are obtained. These stabilized productsare less corrosive to metals, such as iron, and retain their 5 purityand initial color for a much longer time.

It will be understood that many variations and modifications can be madewithout departing from the spirit or scope of my invention. For example,other mercaptans may be eflectively stabilized and other phosphoruscompounds of the class herein disclosed may be substituted for thosespecifically mentioned. Accordingly, my invention is not to be limitedto the specific embodiments disclosed, but I intend to cover myinvention broadly as in the appended claims.

I claim:

1. A composition of matter comprising a mercaptan, normally subject tooxidation by the oxygen of the air, and from about 0.001% to about 1% ofan alkyl acid-ester of an oxygen acid of phosphorus.

2. A composition of matter comprising a mercaptan, normally subject tooxidation by the oxygen of the air, and from about 0.001% to about 1% ofan alkyl acid-ester of phosphoric acid.

3. A composition of matter comprising a mercaptan, normally subject tooxidation by the oxygen of the air, and from about 0.001% to about 1% o!a long chain alkyl acid-ester of phosphoric acid.

4. A composition oi matter comprising a mercaptan, normally subject tooxidation by the oxygen of the air, and from about 0.001% to about 1% ofa mixture of alkyl acid-esters of phosphoric acid {comprisingmono-(n-octyl) phosphate. di-(n-octyl) phosphate, mono-(n-decyl)phosphate and di-(n-decyl) hosphate.

5. A composition of matter comprising a mer captan, which, except forthe -SH group, consists of carbon and hydrogen and which is normallysubject to catalytic oxidation caused by a member of the groupconsisting of iron and its compounds, and from about 0.001% to about 1%of an organic acid-ester of an oxygen acid of phosphorus in which theorganic group consists of carbon and hydrogen.

6. A composition of matter comprising a mercaptan, which, except for the--SH group, consists of carbon and hydrogen and which is normallysubject to catalytic oxidation caused by a member of the groupconsisting of iron and its compounds, and irom about 0.001 to about 1 ofan organic acid-ester of phosphoric acid in which the organic groupconsists of carbon and hydrogen.

'1. A composition of matter comprising a. mercaptan, which, except torthe -SH group, consists of carbon and hydrogen and which is normallysubiect-to catalytic oxidation caused by a member of the groupconsisting of iron and its compounds, and from about 0.001% to about 1%of a long chain alkyl acid-ester of phosphoric acid,

8. A composition of matter comprising a mercaptan, which, except for the-SH group, consists oi carbon and hydrogen and which is normally subjectto catalytic oxidation caused by a member of the group consisting ofiron and its compounds, and from about 0.001% to about 1% of a mixture02 alkyl acid-esters of phosphoric acid comprisng mono-(n-octyl)phosphate, di- (n-octyl) phosphate, mono-(n-decyl) phosphate anddi-(n-decyl) phosphate.

9. A composition oi matter comprising an allphatic mercaptan, which,except for the --SH group, consists of carbon and hydrogen and which isnormally subject to oxidation by the oxygen oi 7 the air, and from about0.001% to about 1% of a lone chain alkyl acid-ester of phosphoric acid.

10. A composition or matter comprising a mixture of mercaptanscomprising n-octyi mercaptan and n-decyl mercaptan, normally subject tooxidation by the oxygen oi the air, and from about 0.001% to about 1% ofan orlanic acid-ester of an oxygen acid of phosphorus in which theorganic group consists of carbon and hydrogen.

11. A composition or matter comprising a mixture oi mercaptanscomprising n-octyl mercaptan and n-decyl mercaptan, normally subject tooxidation by the oxygen of the air, and from about 0.001% to about 1% ofa mixture of alhl acidesters of phosphoric acid comprising mono-(noctyl)phosphate, di-(n-octyi) phosphate, mono- (n-decyl) phosphate and di-(n-decyl) phosphate.

12. A composition of matter comprising a mercaptan, normally subject tooxidation by the oxygen or the air, and from about 0.001 96 to about 1%or a member of the class consisting oi alkyl acid-esters of phosphoricacid, cycloalkyi acidesters of phosphoric acid, monocyclic-aryiacidesters of phosphoric acid, alkyl acid-esters oi phosphorous acid,hydroxy-aikyl phosphonic acid,

monocyclic-aryl phosphonic acid, monocyclicr arylamidoalkyi phosphonicacid, alkylamidoaikyl phosphonic acid. monocyclicaryl phosphinic acid,lecithin and cephalin.

13. A composition of matter comprising a mercaptan, which, except forthe SH group, consists of carbon and hydrogen and which is normaiiysubject to catalytic oxidation caused by a member of the groupconsisting of iron and its compounds, and from about 0.001% to about 1%oi a member oi the class consisting of alkyl acidesters of phosphoricacid, cycloalky! acid-esters oi phosphoric acid, monocyciic-aryiacid-esters oi phosphoric acid, alkyi acid-esters of phosphorous acid,hydroxy-allwl phosphonic acid, monocyclic-aryl phosphonic acid,monocyclicarylamidoalkyl phosphonic acid, alkylamidoalkyl phosphonicacid, monocyclic-aryl phosphinic acid, lecithin and cephalin,

14. A composition or matter comprising a mixture of mercaptanscomprising n-octyl mercaptan and n-decyl mercaptan, normally subject tooxidation by the oxygen 0! the air, and irom about 0.001% to about 1% oia member oi the class consisting of alkyl acid-esters of phosphoricacid, cycloaikyl acid-esters of phosphoric acid, monocyclic-arylacid-esters of phosphoric acid, alkyl acid-esters ot phosphorous acid,hydroxyalkyl phosphonic acid, monocyclic-aryl phosphonic acid,monocyclic-aryiamidoalkyi phosphonic acid, alkylamidoaikyl phosphonicacid, monocyclic-aryl phosphinic acid, lecithin and cephalin.

CHARLES J. PEDERSEN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS 30 Number Name Date 1,593,232 Whitworth July 20,1926 1,812,839 Derby June 30, 1931 2,005,619 Graves June 18, 19352,052,210 Borglin Aug. 25, 1936 2,346,102 Simo Apr. 4, 1944 Certificateof Correction June 22, 1948.

Patent No. 2,443,835.

CHARLES J. PEDERSEN It is hereby certified that errors appear in therinted s ecification of the above numbered patent re uiring correctionas follows: Co umn 3, me 46, for "d-(n-decyl)" read d'i-(n-decyl); coumn 5, line 27, for "ph ous read phosphorus; column 6, line 37, claim 4,for hosphate read phos hate; an thatthe said Letters Patent should beread with these corrections therein t at the same may conform to therecord of the case in the Patent Oflice.

Signed and sealed this 14th day of September, A. D. 1948.

THOMAS F. MURPHY,

Assistant Commissioner of Patents.

7 the air, and from about 0.001% to about 1% of a lone chain alkylacid-ester of phosphoric acid.

10. A composition or matter comprising a mixture of mercaptanscomprising n-octyi mercaptan and n-decyl mercaptan, normally subject tooxidation by the oxygen oi the air, and from about 0.001% to about 1% ofan orlanic acid-ester of an oxygen acid of phosphorus in which theorganic group consists of carbon and hydrogen.

11. A composition or matter comprising a mixture oi mercaptanscomprising n-octyl mercaptan and n-decyl mercaptan, normally subject tooxidation by the oxygen of the air, and from about 0.001% to about 1% ofa mixture of alhl acidesters of phosphoric acid comprising mono-(noctyl)phosphate, di-(n-octyi) phosphate, mono- (n-decyl) phosphate and di-(n-decyl) phosphate.

12. A composition of matter comprising a mercaptan, normally subject tooxidation by the oxygen or the air, and from about 0.001 96 to about 1%or a member of the class consisting oi alkyl acid-esters of phosphoricacid, cycloalkyi acidesters of phosphoric acid, monocyclic-aryiacidesters of phosphoric acid, alkyl acid-esters oi phosphorous acid,hydroxy-aikyl phosphonic acid,

monocyclic-aryl phosphonic acid, monocyclicr arylamidoalkyi phosphonicacid, alkylamidoaikyl phosphonic acid. monocyclicaryl phosphinic acid,lecithin and cephalin.

13. A composition of matter comprising a mercaptan, which, except forthe SH group, consists of carbon and hydrogen and which is normaiiysubject to catalytic oxidation caused by a member of the groupconsisting of iron and its compounds, and from about 0.001% to about 1%oi a member oi the class consisting of alkyl acidesters of phosphoricacid, cycloalky! acid-esters oi phosphoric acid, monocyciic-aryiacid-esters oi phosphoric acid, alkyi acid-esters of phosphorous acid,hydroxy-allwl phosphonic acid, monocyclic-aryl phosphonic acid,monocyclicarylamidoalkyl phosphonic acid, alkylamidoalkyl phosphonicacid, monocyclic-aryl phosphinic acid, lecithin and cephalin,

14. A composition or matter comprising a mixture of mercaptanscomprising n-octyl mercaptan and n-decyl mercaptan, normally subject tooxidation by the oxygen 0! the air, and irom about 0.001% to about 1% oia member oi the class consisting of alkyl acid-esters of phosphoricacid, cycloaikyl acid-esters of phosphoric acid, monocyclic-arylacid-esters of phosphoric acid, alkyl acid-esters ot phosphorous acid,hydroxyalkyl phosphonic acid, monocyclic-aryl phosphonic acid,monocyclic-aryiamidoalkyi phosphonic acid, alkylamidoaikyl phosphonicacid, monocyclic-aryl phosphinic acid, lecithin and cephalin.

CHARLES J. PEDERSEN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS 30 Number Name Date 1,593,232 Whitworth July 20,1926 1,812,839 Derby June 30, 1931 2,005,619 Graves June 18, 19352,052,210 Borglin Aug. 25, 1936 2,346,102 Simo Apr. 4, 1944 Certificateof Correction June 22, 1948.

Patent No. 2,443,835.

CHARLES J. PEDERSEN It is hereby certified that errors appear in therinted s ecification of the above numbered patent re uiring correctionas follows: Co umn 3, me 46, for "d-(n-decyl)" read d'i-(n-decyl); coumn 5, line 27, for "ph ous read phosphorus; column 6, line 37, claim 4,for hosphate read phos hate; an thatthe said Letters Patent should beread with these corrections therein t at the same may conform to therecord of the case in the Patent Oflice.

Signed and sealed this 14th day of September, A. D. 1948.

THOMAS F. MURPHY,

Assistant Commissioner of Patents.

